Section 4: Wastewater discharges

Archived Content

Information identified as archived is provided for reference, research or recordkeeping purposes. It is not subject to the Government of Canada Web Standards and has not been altered or updated since it was archived. Please "contact us" to request a format other than those available.

Archived

Canada has one of the largest renewable water supplies in the world, an
average of 3,472 km3 per year. 1 Rivers, lakes and marine areas are used to dispose of wastewater
and industrial waste, which can have a negative impact on water quality. This
section will examine discharges of municipal and industrial wastewater.

Water discharged into drains or sewers, water received by water treatment
plants or water discharged directly to the environment is all considered wastewater.
Wastewater includes all return flows of water to the environment, regardless
of quality. 2

Municipal wastewater

Municipal wastewater is liquid waste and can be divided into two categories:

sanitary sewage from homes, businesses, institutions and industries;

stormwater from rain or melting snow that drains off rooftops, lawns,
roads, and other urban surfaces.

Wastewater is collected by sewer systems and in most cases is treated before
being released to the environment (see Textbox: Municipal wastewater). 3

Most households in Canada are connected to a municipal sewer system. In 2009, 82%
of households lived in dwellings connected to municipal sewer systems, while 13%
used private septic systems and 1% used communal septic systems. 4

Municipal wastewater

Municipal wastewater can contain grit, debris, suspended solids, disease-causing
pathogens, decaying organic waste, nutrients and about 200 different
identified chemicals. It is a leading source of suspended solids, nutrients,
organic chemicals and metals discharged into Canadian waters. 5

When discharged, municipal wastewater can cause aesthetic problems such
as odours and discolouration. Disease-causing pathogens such as bacteria and
viruses can make water unfit for human use. Excess nutrients can overstimulate
the growth of aquatic plants. Decaying organic waste can use up dissolved
oxygen and threaten the survival of aquatic life. Toxic chemicals can harm
aquatic organisms. Additionally, excessive sedimentation 6 can smother fish feeding and
spawning grounds.

Contaminant levels can be high in untreated sewage, stormwater, and combined
sewer 7 overflows. Even treated sewage may still contain some
harmful substances, although in smaller quantities than in raw sewage.

In 2006, municipalities across the country generated a daily average
of 668 L of wastewater per person served by sanitary sewers. 8 Residential sources accounted
for close to two-thirds of the flow into municipal sewer systems, while the
industrial, commercial, and institutional sector produced 18% of municipal
wastewater flows. Stormwater accounted for 9% of sewer flows and the
remainder (8%) was the result of groundwater infiltration into sewer systems
(Chart 4.1).

In smaller communities, wastewater is primarily produced by the residential
sector, whereas in larger communities their share decreases. For example,
in communities of less than 1,000 people, 71% of wastewater
flow was from residential sources, whereas in those communities with 50,000 to 500,000 people,
only 53% was produced by the residential sector in 2006.

Municipal wastewater treatment and discharge destination

Municipal wastewater can be treated to various degrees before release to
the environment. Secondary mechanical treatment is considered the conventional
treatment process in Canada (see Textbox: Wastewater treatment levels).
Of Canadians served by sanitary wastewater collection systems in 2006,
wastewater was treated at the secondary level or better for 79% of the
population. Almost 2% were not served by wastewater treatment facilities
at all. 9

Surface freshwater was the main destination for 91% of municipal wastewater
discharge in 2006, while 6% was discharged into marine water and 3%
was disposed of using other methods, including infiltration, irrigation, and
evaporation processes. Smaller municipalities were more likely to use these
alternative discharge methods.

Wastewater treatment levels

Municipal wastewater can be treated to various levels, each of which includes
specific activities or technologies as described below:

Primary treatment removes insoluble matter only.

Secondary treatment removes biological impurities from water treated
at the primary level.

Local governments across Canada spent $3.9 billion for sewage
collection and disposal in 2006.10

Industrial wastewater

Industrial wastewater is liquid waste discharged from industrial activities
such as manufacturing, mining and power generation (see Textbox: Industrial
Water Use Survey: Coverage).

Industrial Water Use Survey: Coverage

Unless otherwise specified, Section 4.2 Industrial wastewater uses data from the Industrial Water Use Survey. 11 The target population covered manufacturing and thermal-electric
power generation as well as selected mining industries (coal, metal ore, and
non-metallic mineral mining). The survey did not include wastewater from oil
and gas extraction activities or support activities for mining and oil and
gas extraction.

Industrial wastewater treatment and discharge costs

Industrial wastewater treatment and discharge costs were $532.2 million,
approximately 37% of total industrial water costs in 2009 (Table 4.2).

Manufacturing industries spent $452.2 million on wastewater treatment
and discharge, 41% of their total water costs (Table 4.2). The paper industry accounted for the largest share of this total
at $189.3 million, while the food manufacturing industry spent $91.7 million,
the chemical manufacturing industry spent $72.7 million and the
primary metals manufacturing industry spent $49.3 million on wastewater
treatment and discharge.

Mineral extraction industries spent $70.6 million on wastewater
treatment and discharge, 43% of their total expenditure on water.

Thermal-electric power producers use large quantities of water for cooling,
condensing and steam. The industry spent relatively little ($9.5 million
or 6%) on water treatment and discharge as a proportion of their total
water costs in 2009.

Industrial wastewater discharge destination and treatment

Manufacturing industries discharged most of their wastewater (75%) to surface
freshwater bodies, tidewater (11%) and to public and municipal sewers (10%).
The balance was discharged to groundwater or other points. Of the water discharged
by manufacturers, 38% was not treated before being released. Seventeen
percent of the total discharge received primary treatment, 37% underwent
secondary or biological treatment and 8% underwent tertiary or advanced
treatment.

Mining industries discharged most of their wastewater (73%) to surface
freshwater, while discharging another 11% to tailing ponds and 9%
to groundwater. Metal mines accounted for the largest proportion of wastewater
discharged to tailing ponds. Of the total water discharged by mining operations, 60%
was not treated before discharge, 31% underwent primary or mechanical
treatment and 9% underwent tertiary or advanced treatments.

Thermal-electric power generation industries discharged 95% of their
wastewater to surface freshwater bodies. Almost 59% of this water was
not treated before being discharged.

Industrial water recirculation

Water recirculation is defined as the process of using the same water more
than once in a system. The water must leave the system and re-enter it again
or be used in a different system. Water recirculation reduces the need for
industries to take in new water. 13

In 2009, 7,770.9 million cubic metres of water was recirculated
by the manufacturing, mining and thermal electric power generation industries.
The recirculation rate, defined as the amount of recirculated water as a percent
of water intake, was 25%.

Manufacturing industries recirculated 2,003.3 million cubic metres
of water, 53% of their total water intake. The primary metal manufacturing
industry had a recirculation rate of 98%.

Mining industries reported the use of 1,547.7 million cubic metres
of recirculated water in 2009, a recirculation rate of 311%. Almost
all of the recirculated water (98%) was used for process activities by the
mining industry.

Thermal-electric power producers recirculated 4,220.0 million
cubic metres of water, resulting in a recirculation rate of 16%.

Industrial water pollutant discharges

Ammonia and nitrate made up 90% of the total tonnage of substances
released into water by industrial facilities in Canada in 2009 according
to the NPRI database (Table 4.3).

In 2008, $114.7 million in capital expenditures was invested
in pollution abatement and control processes and technologies to reduce emissions
to surface water, while capital expenditures on pollution prevention processes
and technologies totalled $178.8 million (Table 4.4).

The paper manufacturing industry spent the greatest portion (34%) of their
total capital expenditures on pollution abatement and control to reduce emissions
to surface water, followed by the food manufacturing (19%) and chemical manufacturing
(17%) industries. The mining and quarrying industry spent the greatest portion
(62%) of their total capital expenditures on pollution prevention to reduce
emissions to surface water.